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Scientists seek a safe level for taconite fibers

The questions go back 30 years to the days when Reserve Mining was dumping its waste rock in Lake Superior. Microscopic particles from the rock turned up in the drinking water in Duluth and other cities along the North Shore. Scientists from the Environmental Protection Agency said they were similar to asbestos, a substance known to cause cancer and other serious health problems.

Minnesota and the federal government sued Reserve to get it to stop dumping in Lake Superior.

Northshore plantMPR Photo/Stephanie Hemphill

Dr. Hillary Carpenter, a toxicologist at the Minnesota Department of Health, has studied the case. He says government experts told the court they could see no difference between the particles from Reserve and deadly asbestos fibers.

"You can't look at it under a microscope and say it's not commercial asbestos," he says. "And so the court's decision basically said, 'If you can't tell the difference, if you can't tell me the difference, it's all the same.'"

In a landmark decision, the court ordered Reserve to stop dumping in the lake. It also said the mine shouldn't pollute the air with the fibers either. It set up a comparison city. The court said the fiber count in Silver Bay, next to the processing plant, couldn't be any higher than in St. Paul.

The company installed pollution control equipment, and the number of fibers in Silver Bay went way down. They went lower than the fiber count in St. Paul.

At some point, no one quite remembers when, the state stopped measuring the fibers in St. Paul.

But to this day, Northshore Mining, Reserve's successor, monitors the air on the hillside between the plant and the town of Silver Bay.

Scott GischiaMPR Photo

Scott Gischia is an environmental manager at Northshore Mining. He's standing by a large box that holds the equipment.

"It's a computer-controlled sampler," he explains. "It's monitoring flow, ambient temperature, and ambient pressure. And that information feeds into what the final concentration of fibers are, that's collected on the sampler."

Gischia collects the filter from this sampler every 21 days, and sends it for analysis to the Health Department in St. Paul.

The records show a consistent reduction in fibers over the years, as the plant installed more and more pollution control equipment.

The mine has always maintained that there is a difference between commercial asbestos and the fibers in its ore. Scott Gischia says the two have similar chemical compositions, but the taconite dust produces more of a fragment than a fiber.

"I think there's a clear difference between a long, thin, flexible fiber, and a short, blocky cleavage fragment," he says.

But that physical difference doesn't matter, according to Dr. Phil Cook. Cook was one of the EPA scientists who testified in the original Reserve court case.

Phil CookMPR Photo/Stephanie Hemphill

Cook did studies on rats to see which types of fibers caused cancer, and at what doses.

Using electron microscopes, which were new at the time, he learned that the particles found in Northshore's ore did cause lung cancer in rats. And that some of those fragments divided even more once they were in the rats' lungs.

"So there was some kind of slow leaching going on while the fibers were in tissue, and blocky particles would become thinner fibers," he says. "So the number of fibers was increasing, and the dose was increasing."

In other words, the longer the particles were in the body, the more dangerous they became.

In the years since then, Cook has collected information from many animal studies, and now he's assembled it into a data base that will form the foundation of a health-based standard.

Hillary CarpenterMPR Photo

The Health Department's Hillary Carpenter says it includes information about all kinds of fibers and fragments.

"This data base will allow us to manipulate the data in such a way that we can make comparisons between fiber sizes and fiber types, to allow us to compare the relative potencies of fibers," says Carpenter.

The next step is to extrapolate that information on animals, to create a model for human exposure.

Then, the Health Department will set a standard for how many of the fibers should be allowed in the air.

The process is expected to take at least a year.

In the meantime, two environmental groups have filed notice of intent to sue Northshore Mining for violating that court-ordered permit.